Sodium metabisulfite is commonly used to precipitate dissolved gold out aqua regia and gold chloride solutions. This is done by adding it to a solution containing gold ions and heating the mixture, causing the sodium metabisulfite to react with the gold ions and reduce them to elemental gold, which will then be precipitated out of the solution. Sodium metabisulfite is a popular choice in this process because it is more selective in precipitating gold by itself.
In the process of gold extraction from scrap computer electronics parts, Sodium Metabisulfite is usually used along with Urea.
Urea, also called carbamide. In gold recovery processes, it is used as a neutralizer of excess nitric acid in aqua regia solutions. Urea reacts with the nitric acid to form nitrogen gas and water, which reduces the acidity of the solution. It is important to ensure that the solution does not become too acidic, as this can cause the gold to be oxidized and lose some of its value.
To make aqua regia solution you will need hydrochlorid acid and nitric acid. These are not included in this kit.
This kit is a convenient way to obtain some of the chemicals used in scrap gold recovery. Please follow your own instructions for performing gold and other precious metals precipitation from aqua regia solution.